During the tenure of the next granting period, I hope to continue the studies to further quantitate cellular NAD levels, relate these levels to the functioning of NAD-related metabolic pathways, and especially to extend this approach to the Talpid mutant material. The general emphasis of our approach is an attempt to correlate cytoplasmic events, both the synthesis and degradation of NAD and energy related pathways, with the expressivity of the developing limb mesodermal cells from both normal and Talpid donors. We hope to provide a quantitative basis for our general speculations that NAD has a controlling role in the phenotypic expression of limb mesodermal cells by measuring the cellular NAD levels as well as the functioning of various NAD- related metabolic pathways. It is hoped that specific temporal correlations can be established. With this information and with our ability to use certain NAD-related teratogens we hope to better understand the control of both abnormal and normal development.